Dongfan "Greg" Chung was convicted in July of six counts of economic espionage and other federal charges for having 300,000 pages of sensitive papers in his home. (Christina House/The Orange County Register/Associated Press)

A Chinese-born engineer was sentenced Monday to more than 15 years in prison for hoarding sensitive information about the U.S. space shuttle that prosecutors say he intended to share with China.

The case against Dongfan "Greg" Chung was the United States' first trial on economic espionage charges. The 74-year-old former Boeing Co. engineer was convicted in July of six counts of economic espionage and other federal charges for keeping 300,000 pages of sensitive papers in his home.

Before sentencing Chung in Santa Ana, Calif., U.S. District Judge Cormac J. Carney said he didn't know exactly what information Chung passed to China. "But what I do know is what he did, and what he did pass, hurt our national security and it hurt Boeing," the judge said.

Carney said Chung's scheme with the Chinese government spanned 30 years. During brief remarks, Chung begged the judge to give him a lenient sentence.

"Your honour, I am not a spy, I am only an ordinary man," he said, adding that he had brought the Boeing documents home to write a book.

"I love this country …Your honour, I beg your pardon and let me live with my family peacefully."

Despite Chung's age, prosecutors requested a 20-year sentence, in part to send a message to other would-be spies.

But the judge said he couldn't put a value on the amount of information that Chung stole and couldn't determine exactly how much the breaches hurt Boeing and the nation. He also cited the engineer's age and frail health in going with a sentence of 15 years and eight months.

"It's very difficult having to make a decision where someone is going to have to spend the rest of their adult life in prison," Carney said. "I take no comfort or satisfaction in that."

Assistant U.S. Attorney Greg Staples noted in sentencing papers that Chung amassed a personal wealth of more than $3 million US while betraying his adopted country.

"The [People's Republic of China] is bent on stealing sensitive information from the United States and shows no sign of relenting," Staples wrote. "Only strong sentences offer any hope of dissuading others from helping the PRC get that technology."

Chung's attorney, Thomas Bienert Jr., has said his client will appeal.

The government said investigators found papers stacked throughout Chung's house that included sensitive information about a booster rocket fuelling system — documents that employees were ordered to lock away at the end of each day. The government said Boeing invested $50 million in the technology over a five-year period.

During the non-jury trial, Chung's lawyers argued that he may have violated Boeing policy by bringing the papers home, but he didn't break any laws by doing so, and the U.S. government couldn't prove he had given secret information to China.

In his ruling, Carney wrote that the notion that Chung was merely a pack rat was "ludicrous" and said the evidence showed that he had been passing information to Chinese officials as a spy.

The government believes Chung began spying for the Chinese in the late 1970s, a few years after he became a naturalized U.S. citizen and was hired by Rockwell.

Chung worked for Rockwell until it was bought by Boeing in 1996. He stayed with the company until he was laid off in 2002, then was brought back a year later as a consultant. He was fired when the FBI began its investigation in 2006.